Latent Variables Path (LVP) models have been found to be a helpful device for the formulation and validation of complex theories in educational sciences. The estimation of parameters for LVP models can use the Maximum Likelihood (ML) or the Partial Least Squares (PLS) method. This paper focusses on the PLS method introduced by H. Wold, and compares it to the LISREL method introduced by K.G. Joereskog. The differences in the results are explained by the differences in the statistical assumptions, and some clues to the choice of ML or PLS are given. Several select applications show the range where only PLS estimation is applicable. (Author)